1. Field of the Invention
The present invention relates to molding machines. More specifically, the invention relates to quick change inserts provided in the cavity of a mold.
2. Description of the Related Art
The process of blow molding plastic containers is susceptible to many environmental and process variables, such as temperature, moisture, and pressure. These variables will affect the apparent volume of the container once filled with liquid. If the volume of the container is slightly larger than designed, the container may not appear full when the specified amount of liquid is dispensed into the container. For example, if the volume of a milk container is larger than one gallon, when the container is properly filled with one gallon of milk, the container will appear to be less than full, and a consumer might assume that the container has less than a full gallon of milk and not purchase that container. Therefore it is commercially undesirable for containers to appear less than full.
One method developed to adjust the apparent volume of the container locates an insert in the mold to change the volume of the mold cavity. In the past, this was accomplished by bolting a simple mechanical insert into the cavity of the mold. This had the disadvantage that the bolt fastening the insert would often be accessible only from the back of the mold, requiring complete removal of the mold from the machine in order to change the mold insert.
Another method that emerged for adjusting the volume of blow molded containers is to have the position of the insert adjusted by a pneumatic control. Using this method, pneumatic pressure is adjusted to extend or retract the insert relative to the surface of the mold cavity. The disadvantage of the pneumatic method is that the installation and removal of the insert requires a complex procedure and special tools, including a pneumatic pump. Additionally, there is a risk that the insert can fall out of the mold if the insert is not correctly installed or if the pneumatic system loses pressure, since a continuous vacuum draw is not provided.
In view of the above, there exists in the industry a need for volume control inserts that are readily accessible, can be quickly changed and do not require specific tools for changing them.